1. Field of the Invention
The present invention is generally in the field of semiconductor fabrication. More specifically, the invention is in the field of fabrication of capacitors in semiconductor dies.
2. Background Art
High performance mixed signal and RF circuits require high density integrated capacitors. Metal-insulator-metal (xe2x80x9cMIMxe2x80x9d) capacitors can be considered for use in the fabrication of integrated mixed signal and RF circuits on semiconductor dies. Disadvantageously, typical MIM capacitors have low capacitance density and since RF and mixed signal applications require high capacitance values, the die area consumed by typical MIM capacitors is too large and results in increased die costs to the manufacturer and the user.
Moreover, semiconductor dies that include typical MIM capacitors pose significant problems for interconnect routing because the metal plates used in the MIM capacitors prevent effective utilization of interconnect metal layers for their primary purpose, i.e. for interconnect routing. For example, use of several MIM capacitors or one large MIM capacitor would significantly hinder interconnect routing in a die. The reason is that large MIM capacitor plates would result in smaller available area for interconnect lines and would also require longer interconnect lines taking a xe2x80x9cdetourxe2x80x9d around the large obstacles created by MIM capacitor plates present in the same interconnect metal layer where interconnect routing is to take place. Thus, lack of interconnect design flexibility and undesirably long interconnect lines, as well as consumption of significant die area by MIM capacitor plates are significant drawbacks in the use of MIM capacitors in mixed signal and RF applications.
Therefore, a need exists for mixed signal and RF MIM capacitors that are dense and that further do not adversely affect interconnect routing.
The present invention is directed to a high density composite MIM capacitor with flexible routing in semiconductor dies. The invention overcomes the need in the art for mixed signal and RF MIM capacitors that are dense and that do not adversely affect interconnect routing. The invention achieves a composite MIM capacitor having a capacitance with significantly improved density by building a composite MIM capacitor perpendicular to the surface of the die. Moreover, the present invention advantageously increases routing capability because the composite MIM capacitor is fabricated by utilizing the space amply available between interconnect metal layers and without significant use of interconnect metal layers.
According to one embodiment of the invention, a structure comprises an electrode of a lower MIM capacitor situated in a first interconnect metal layer of a semiconductor die. The first interconnect metal layer can be, for example, aluminum or copper, and is situated over a first interlayer dielectric layer. The structure further comprises a shared electrode of the lower MIM capacitor and an upper MIM capacitor. The shared electrode is situated above the electrode of the lower MIM capacitor and can comprise, for example, titanium nitride, tantalum nitride, or a stack comprising aluminum and titanium nitride or tantalum nitride. The structure further comprises an electrode of the upper MIM capacitor situated over the shared electrode. The electrode of the upper MIM capacitor is coupled to the electrode of the lower MIM capacitor through vias and a second interconnect metal layer. The electrode of the upper MIM capacitor can comprise, for example, titanium nitride or tantalum nitride.
The structure also comprises a lower MIM dielectric layer situated between the electrode of the lower MIM capacitor and the shared electrode; and an upper MIM dielectric layer situated between the shared electrode and the electrode of the upper MIM capacitor. The lower and upper MIM dielectric layers can comprise a high-k dielectric, for example, silicon nitride, tantalum pentoxide, aluminum oxide, hafnium oxide, zirconium oxide, zirconium aluminum silicate, hafnium silicate, hafnium aluminum silicate or other dielectrics with a relatively high dielectric constant. The structure further comprises a second interlayer dielectric layer situated between the first interconnect metal layer and the second interconnect metal layer. The second interlayer dielectric layer may comprise silicon oxide or a low-k dielectric, for example, porous silica, fluorinated amorphous carbon, fluoro-polymer, parylene, polyarylene ether, silsesquioxane, fluorinated silicon dioxide, or diamond-like carbon. The structure further comprises multiple vias situated in the second interlayer dielectric layer, wherein the multiple vias connect the electrodes of the lower and upper MIM capacitors to the second interconnect metal layer. The multiple vias can be, for example, tungsten or copper. The structure may further comprise multiple metal segments situated in the second interconnect metal layer. The multiple metal segments and multiple vias provide connectivity between the electrodes of the lower and upper MIM capacitors. In one embodiment, the electrode of the upper MIM capacitor can be divided into two or more segments to allow additional paths for connectivity to reduce the resistance of an electrode of the composite MIM capacitor. In other embodiments, the present invention is a method for fabricating various embodiments of the composite MIM capacitor. Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following description and accompanying drawings.